The present invention relates to novel high pigment/low viscosity nail polish compositions and a process for preparing the same.
Typical prior art processes for the preparation of pigments in a form suitable for use in nail polish compositions generally involve individually milling mixtures of a suitable pigment in alcohol wet cellulose nitrate and plasticizer to provide nitrocellulose-pigment chips. Such processes are generally known in the art as "chipping" and given the explosive property of nitrocellulose are both hazardous and limited to specialized milling techniques. More specifically, the prior art "chipping" process can only safely be carried out as long as the alcohol remains in intimate contact with the nitrocellulose in sufficient quantities to prevent the mixture from being ignited by the heat evolved during milling. As a practical consequence, the "chipping" process is inherently limited in the extent to which the pigment can be ground or milled. Moreover, the pigment chips produced in accordance with the prior art technology are highly flammable, thereby necessitating special shipping, storage and handling procedures.
Apart from the aforementioned problems, the utilization of the nitrocellulose-pigment chips in the manufacture of nail polish compositions presents other difficulties, principally due to the fact that the cellulose nitrate increases the viscosity of the final coating formula in direct proportion to the amount of pigment present therein. Compositions which utilize large amounts of pigment necessarily contain large amounts of cellulose nitrate, which in turn necessitate thinning in order to obtain a suitably brushable final product. Thinners, however reduce the pigment and polymer solids concentration and hence, their use is counter productive to obtaining a final product having acceptable coverage properties. Moreover, in preparing nail polish compositions, the nitrocellulose pigment chips generally require additional processing prior to incorporation into a suspension base lacquer, e.g., the chips must first be redissolved in a lacquer thinner to provide a solvent based paste. Change in pigment concentrations as a result of thinning, solvent loss or pigment settling are frequent problems encountered in the prior art techniques of preparing high quality nail polishes.
Other known techniques and equipment used in preparing suitable pigment dispersions (homogenizers, media mills (sand and ball mills) and colloid mills) require diluting the nitrocellulose grinding medium with flammable solvents in order to obtain a suitable viscosity. These processes suffer similar problems due to poor size control of the pigment particle; flammability; low percentage pigment concentrations due to viscosity considerations; and destruction of cellulose nitrate polymer molecule attributable to high-shear milling.